The present invention relates to sputtering targets and their methods of manufacture.
A sputtering chamber is used to sputter deposit material onto a substrate to manufacture electronic circuits, such as for example, integrated circuit chips and displays. Typically, the sputtering chamber comprises an enclosure wall that encloses a process zone into which a process gas is introduced, a gas energizer to energize the process gas, and an exhaust port to exhaust and control the pressure of the process gas in the chamber. The chamber is used to sputter deposit a material from a sputtering target onto the substrate, such as a metal for example, aluminum, copper, tungsten or tantalum; or a metal compound such as tantalum nitride, tungsten nitride or titanium nitride. In the sputtering processes, the sputtering target is bombarded by energetic ions, such as a plasma, causing material to be knocked off the target and deposited as a film on the substrate.
In one version, a sputtering target may be formed by holding a sheet of spin-formed sputtering material against the surface of a target backing plate and diffusion-bonding the sputtering material to the backing plate by hot isostatic pressing. However, this method has several disadvantages. The sputtering material required to form the spin-formed sheet typically has to have a high level of purity, and consequently, is expensive. Target fabrication costs are driven even higher because both surfaces of the sheet of sputtering material are typically machined smooth to facilitate diffusion bonding to the underlying backing plate as well as to provide a smooth exposed sputtering surface. Targets formed by such a method can be undesirable because they can have a grain structure that is sheared by the forces generated in the spin-forming process, resulting in non-uniform grain sizes. Also, the targets can have undesirable pores and voids occurring in the bond between the backing plate and sputtering material. During processing, the non-uniform grain size and voids of the target can generate sputtered deposits that are non-uniform or uneven in thickness. The non-uniform and uneven deposition of the sputtered material can result in processed substrates having inferior quality, and can even damage structures formed on the substrate.
It is also difficult to form sputtering targets having convoluted or complex shapes using conventional processes. Targets having complex shapes are often used to provide enhanced sputtering coverage in magnetic fields, as described for example in U.S. Pat. No. 6,274,008 to Gopalraja et al., “Integrated Process for Copper Via Filling,” commonly assigned to Applied Materials, which is incorporated herein by reference in its entirety. Such targets may comprise for example ridges, projections, rings, troughs, recesses and grooves. Conventional processes such as the spin forming process are not satisfactory in forming complex target shapes, because a significant amount of machining is required to cut out the desired convoluted shape from the spin formed layer. This machining is costly and wastes the expensive high purity sputtering material. Also, excessive machining can generate shearing forces on the surface of the target which plastically deform the grains on the target surface to produce an undesirable surface grain structure.
Thus, it is desirable to form sputtering targets having more uniform and consistent grain surface structure and with fewer voids. It is further desirable to form sputtering targets having complex or non-planar shapes reproducibly and with reduced costs.